/lianghe_work/article/details/46519633
与多线程、多进程相比，I/O复用最大的优势是系统开销小，系统不需要建立新的进程或者线程，也不必维护这些线程和进程。
代码示例：
#include <stdio.h> #include <unistd.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <sys/socket.h>#include <sys/types.h>#include <netinet/in.h>#include <arpa/inet.h>#include <sys/select.h> #define SERV_PORT 8080#define LIST 20 //服务器最大接受连接#define MAX_FD 10 //FD_SET支持描述符数量 int main(int argc, char *argv[]){ int sockfd; int err; int i; int connfd; int fd_all[MAX_FD]; //保存所有描述符，用于select调用后，判断哪个可读 //下面两个备份原因是select调用后，会发生变化，再次调用select前，需要重新赋值fd_set fd_read; //FD_SET数据备份fd_set fd_select; //用于select struct timeval timeout; //超时时间备份 struct timeval timeout_select; //用于select struct sockaddr_in serv_addr; //服务器地址 struct sockaddr_in cli_addr; //客户端地址socklen_t serv_len;socklen_t cli_len; //超时时间设置timeout.tv_sec = 10;timeout.tv_usec = 0; //创建TCP套接字sockfd = socket(AF_INET, SOCK_STREAM, 0); if(sockfd < 0){perror("fail to socket");exit(1);} // 配置本地地址memset(&serv_addr, 0, sizeof(serv_addr));serv_addr.sin_family = AF_INET; // ipv4serv_addr.sin_port = htons(SERV_PORT); // 端口， 8080serv_addr.sin_addr.s_addr = htonl(INADDR_ANY); // ip serv_len = sizeof(serv_addr); // 绑定err = bind(sockfd, (struct sockaddr *)&serv_addr, serv_len); if(err < 0){perror("fail to bind");exit(1);} // 监听err = listen(sockfd, LIST); if(err < 0){perror("fail to listen");exit(1);} //初始化fd_all数组memset(fd_all, -1, sizeof(fd_all)); fd_all[0] = sockfd; //第一个为监听套接字 FD_ZERO(&fd_read); // 清空FD_SET(sockfd, &fd_read); //将监听套接字加入fd_read int maxfd = fd_all[0]; //监听的最大套接字 while(1){ // 每次都需要重新赋值，fd_select，timeout_select每次都会变fd_select = fd_read;timeout_select = timeout; // 检测监听套接字是否可读，没有可读，此函数会阻塞 // 只要有客户连接，或断开连接，select()都会往下执行err = select(maxfd+1, &fd_select, NULL, NULL, NULL); //err = select(maxfd+1, &fd_select, NULL, NULL, (struct timeval *)&timeout_select); if(err < 0){perror("fail to select");exit(1);} if(err == 0){printf("timeout\n");} // 检测监听套接字是否可读 if( FD_ISSET(sockfd, &fd_select) ){//可读，证明有新客户端连接服务器 cli_len = sizeof(cli_addr); // 取出已经完成的连接connfd = accept(sockfd, (struct sockaddr *)&cli_addr, &cli_len); if(connfd < 0){perror("fail to accept");exit(1);} // 打印客户端的 ip 和端口 char cli_ip[INET_ADDRSTRLEN] = {0};inet_ntop(AF_INET, &cli_addr.sin_addr, cli_ip, INET_ADDRSTRLEN);printf("----------------------------------------------\n");printf("client ip=%s,port=%d\n", cli_ip,ntohs(cli_addr.sin_port)); // 将新连接套接字加入 fd_all 及 fd_read for(i=0; i < MAX_FD; i++){ if(fd_all[i] != -1){ continue;}else{fd_all[i] = connfd;printf("client fd_all[%d] join\n", i); break;}} FD_SET(connfd, &fd_read); if(maxfd < connfd){maxfd = connfd; //更新maxfd} } //从1开始查看连接套接字是否可读，因为上面已经处理过0（sockfd） for(i=1; i < maxfd; i++){ if(FD_ISSET(fd_all[i], &fd_select)){printf("fd_all[%d] is ok\n", i); char buf[1024]={0}; //读写缓冲区 int num = read(fd_all[i], buf, 1024); if(num > 0){ //收到 客户端数据并打印printf("receive buf from client fd_all[%d] is: %s\n", i, buf); //回复客户端num = write(fd_all[i], buf, num); if(num < 0){perror("fail to write ");exit(1);}else{ //printf("send reply\n");} } else if(0 == num){ // 客户端断开时 //客户端退出，关闭套接字，并从监听集合清除printf("client:fd_all[%d] exit\n", i);FD_CLR(fd_all[i], &fd_read);close(fd_all[i]);fd_all[i] = -1; continue;} }else { //printf("no data\n"); }}} return 0;}
运行结果：
